1. Field of the Invention
This invention relates to a process for preparing hexamethyleneimine from hexamethylenediamine at low temperatures and pressures, and more specifically, to a process for preparing hexamethyleneimine from hexamethylenediamine which comprises catalytically deaminating hexamethylenediamine in an inert solvent, and continuing the reaction while removing the resulting hexamethyleneimine immediately from the reaction system.
2. Description of the Prior Art
Hexamethyleneimine is an important compound which is useful as an intermediate material for pharmaceuticals and agricultural chemicals, and also finds a wide range of applications as rubber vulcanization accelerators and other rubber chemicals, ingredients for textile lubricants, antistatic agents and finishing agents, corrosion inhibitors for metals, and modifiers or crosslinking agents for resins.
Heretofore, hexamethyleneimine has been obtained in small quantities from by-products which occur in the production of hexamethylenediamine by catalytic hydrogenation of adiponitrile or in the production of hexamethylenediamine by catalytic ammonolysis of 1,6-hexanediol. It has also been reported in Journal of the Chemical Society of Japan, Vol. 82, page 1701 (1961) that hexamethyleneimine was obtained in a yield of about 10% by heating hexamethylenediamine together with Raney nickel at 160.degree. to 170.degree. C., but a greater part of the product consisted of a resinous product or tar.
Chemische Berichte, Vol 96, page 924 (1963) also discloses that by heating hexamethylenediamine together with Raney nickel at 142.degree.-143.degree. C. in a solvent such as benzene, xylene or mesitylene, hexamethyleneimine is obtained in a yield of 24 to 38% (as the picrate salt), but at the same time, 1,6-bis-hexamethyleneiminohexane is formed in a yield of 12 to 47% (as the picrate salt). Furthermore, Canadian Pat. No. 920,606 (1973) discloses that hexamethyleneimine is obtained in a selectivity of 47 to 87% by contacting hexamethylenediamine with a hydrogenation catalyst at 150.degree. to 250.degree. C. in the presence of hydrogen. However, since the conversion of hexamethylenediamine is as low as 17 to 44%, a large quantity of unreacted hexamethylenediamine must be recovered by distillation. It is also necessary to reduce the amounts of by-products by adding hydrogen and ammonia during the reaction.